I just ordered the 3GS, upgrading from a 1st gen. iPhone. Nowhere on my confirmation does it mention that it's an upgrade from an existing phone, rather than adding an additional phone to my existing plan. When I plug the new phone into my mac, iTunes will want to activate using my same #, without me moving the sim? Or do I put the old sim in the new phone?

MacRumors attracts a broad audience
of both consumers and professionals interested in
the latest technologies and products. We also boast an active community focused on
purchasing decisions and technical aspects of the iPhone, iPod, iPad, and Mac platforms.